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<!DOCTYPE html>
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<title>Etlas: e-paper dashboard</title>
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<h2 class="center" id="title">ETLAS: E-PAPER DASHBOARD</h2>
<h5 class="center">05 SEPTEMBER 2024</h5>
<br>
<div class="twocol justify"><p>Repurposed the <a href="../e-reader/">e-reader</a> into something for regular use. News,
stocks, weather dashboard. ESP32 NodeMCU D1 + 7.5” Waveshare e-paper + DHT22
sensor.</p>
<table style="border: none;">
<tr style="border: none;">
<td style="border: none;"><img src="dash.jpg" alt="front" style="width: 100%" /></td>
<td style="border: none;"><img src="pcb.jpg" alt="back" style="width: 100%" /></td>
</tr>
<tr style="border: none;">
<td colspan="2" style="border: none;"><img src="etlas_arch.png" alt="front" style="width: 100%" /></td>
</tr>
</table>
<p>Stocks: Two weeks EOD data from Polygon.io (max possible). Flask app on VPS
manages watchlist, relays the feed. Backend: httpd + htpasswd + slowcgi +
Flask.</p>
<p>gui_plot_stocks() plots a stepped graph; was easier to implement, but the code
is hideous; triggers watchdog. vTaskDelay() prevents that.</p>
<p>NOTE: Refactor. Bresenham’s?</p>
<p>News: Channel NewsAsia RSS. MCU does the parsing. Didn’t plan to have a backend
at the time. Now that I have one for stocks, should relay the feed for
flexibility.</p>
<p>Weather: DHT22 single-wire protocol. 26µs/50µs/70µs pulses are too fast for
standard ESP32 APIs. Bit-banged relative pulse widths (ported from <a href="https://github.com/Fonger/ESP8266-RTOS-DHT" class="external" target="_blank" rel="noopener noreferrer">ESP8266</a>):</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>static inline int dht_await_pin_state(int state, int timeout)
{
int t;
static const uint16_t delta = 1;
for (t = 0; t < timeout; t += delta) {
ets_delay_us(delta);
if (gpio_get_level(DHT_PIN) == state)
return t;
}
return 0;
}
static inline int dht_get_raw_data(unsigned char buf[BUFLEN])
{
int rc;
unsigned char i, pwl, pwh;
gpio_set_level(DHT_PIN, 0);
ets_delay_us(1100);
gpio_set_level(DHT_PIN, 1);
if (!dht_await_pin_state(0, 40)) {
rc = 1;
xQueueSend(dht_evt_queue, &rc, (TickType_t) 0);
return 0;
}
if (!dht_await_pin_state(1, 80)) {
rc = 2;
xQueueSend(dht_evt_queue, &rc, (TickType_t) 0);
return 0;
}
if (!dht_await_pin_state(0, 80)) {
rc = 3;
xQueueSend(dht_evt_queue, &rc, (TickType_t) 0);
return 0;
}
for (i = 0; i < BUFLEN; i++) {
if (!(pwl = dht_await_pin_state(1, 50))) {
rc = 4;
xQueueSend(dht_evt_queue, &rc, (TickType_t) 0);
return 0;
}
if (!(pwh = dht_await_pin_state(0, 70))) {
rc = 5;
xQueueSend(dht_evt_queue, &rc, (TickType_t) 0);
return 0;
}
buf[i] = pwh > pwl;
}
return 1;
}
</code></pre></div></div>
<p>epd_init() stalls intermittently on first refresh() after flash. Toggling delay
values in refresh() resolves it. If the first refresh succeeds, it remains
stable. Root cause unknown–suspect noisy power supply due to powering display
via MCU.</p>
<p>Uptime: August 2024 - January 2026</p>
<p>Commit:
<a href="https://git.asciimx.com/etlas/commit/?id=a92c86ac1592c2137d3d1fec1668eacc2d0ca581">a92c86a</a></p>
</div>
<p class="post-author right">by W. D. Sadeep Madurange</p>
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